Technologies for Wastewater and Sludge Treatment

This study examined the impact of adding bentonite clay (concentration of 1.5 to 10 g/L) to a pilot-scale aerobic ceramic membrane bioreactor (AeCMBR) for treating pharmaceutical wastewater (PhWW). The hydraulic retention time (HRT) was maintained at 24 h; the dissolved oxygen was between 2 mg/L (on) and 4 mg/L (off) throughout operation. Organic and nitrogen pollution removal rates and heavy metal (Cu, Ni, Pb, Zn) reduction rates were assessed. The chemical oxygen demand (COD) removal efficiency exceeded 82%. Adsorption improved ammonia (NH4+) removal to 78%; the addition of 5 g of bentonite resulted in a 38% improvement compared with the process without bentonite. The average nitrate concentration decreased from 169.69 mg/L to 43.72 mg/L. The average removal efficiencies for Cu, Ni, Pb and Zn were 86%, 68.52%, 46.90% and 56.76%, respectively. Bentonite at 5 g/L significantly reduced membrane fouling. The cost–benefit analysis enabled us to predict that the process will meet the multiple objectives of durability, treatment performance and economic viability. The combination of an AeCMBR and bentonite adsorption has proven to be a valuable solution for treating highly polluted wastewater. Full article

With the rapid development of industry, the discharge of heavy metal-containing wastewater poses a significant threat to aquatic and terrestrial environments as well as human health. This paper provides a brief introduction to the basic principles of ion-imprinted polymer preparation and focuses on the interaction between template ions and functional monomers. We summarized the current research status on typical heavy metal ions, such as Cu(II), Ni(II), Cd(II), Hg(II), Pb(II), and Cr(VI), as well as metalloid metal ions of the As and Sb classes. Furthermore, it discusses recent advances in multi-ion-imprinted polymers. Finally, the paper addresses the challenges faced by ion-imprinted technology and explores its prospects for application. Full article

This study explores the effectiveness of an integrated anaerobic membrane bioreactor (AnMBR) coupled with an anoxic/oxic membrane bioreactor (A/O MBR) for the treatment of natural rubber industry wastewater with high sulfate, ammonia, and complex organic contents. This study was conducted at the lab-scale over a duration of 225 days to thoroughly investigate the efficiency and sustainability of the proposed treatment method. With a hydraulic retention time of 6 days for the total system, COD reductions were over 98%, which reduced the influent from 22,158 ± 2859 mg/L to 118 ± 74 mg/L of the effluent. The system demonstrates average NH₃-N, TN, and total phosphorus (TP) removal efficiencies of 72.9 ± 5.7, 72.8 ± 5.6, and 71.3 ± 9.9, respectively. Despite an average whole biological system removal of 50.6%, the anaerobic reactor eliminated 44.9% of the raw WW sulfate. Analyses of membrane fouling revealed that organic fouling was more pronounced in the anaerobic membrane, whereas aerobic membrane fouling displayed varied profiles due to differential microbial and oxidative activities. Key bacterial genera, such as Desulfobacterota in the anaerobic stage and nitrifiers in the aerobic stage, are identified as instrumental in the biological processes. The microbial profile reveals a shift from methanogenesis to sulfide-driven autotrophic denitrification and sulfammox, with evidence of an active denitrification pathway in anaerobic/anoxic conditions. The system showcases its potential for industrial application, underpinning environmental sustainability through improved wastewater management. Full article

Copper-containing sludge is a common by-product of industrial activities, particularly electroplating and metal processing. This type of sludge contains high concentrations of heavy metals such as copper, which can pose a potential threat to the environment. Therefore, its treatment and disposal require special attention. Due to its efficient mass and heat transfer characteristics, the suspended state technology has shown significant potential for application in a number of key processes, including the drying, decomposition, and reduction of copper-containing sludge. This paper presents an in-depth analysis of the current status of the application of the suspended state technology in the treatment of copper-containing sludge. Based on this analysis, a device for the treatment of copper-containing sludge in the suspended state was designed, through which the characteristics of copper-containing sludge in the oxidative decomposition and reduction phases are investigated. The research objects were gas concentration, temperature, contact state, and particle size time. Orthogonal experiments were initially employed to investigate the relationship between the influencing factors and the conversion rate of copper oxides. This was followed by a single-factor influence study, which led to the determination of the optimal process parameters for the decomposition experiments of the Cu-containing sludge in an oxidizing atmosphere. The 100 μm Cu-containing sludge was reacted with 10% O₂ gas at a flow rate of 1 m/s for 3 min under the condition of 900 °C. The process parameters were then determined as follows: The research objects were gas concentration, temperature, contact state, and particle size time. Orthogonal experiments were employed to investigate the relationship between the influencing factors and the copper conversion rate. This was followed by a single-factor influence study, which determined the optimal process parameters for the copper-containing sludge reduction experiments. The 200 μm copper-containing sludge was reacted for 5 min at a flow rate of 7% carbon monoxide at a flow rate of 1.5 m/s under the condition of 800 °C. Full article

Membrane bioreactors (MBRs) have gained attraction in municipal wastewater treatment because of their capacity to meet strict water quality standards and support water reuse. Despite this, their operational sustainability is often compromised by high resource consumption, especially regarding the use of chemicals for membrane cleaning. This study explores innovative membrane-cleaning strategies to enhance the sustainability of MBR processes. Through long-term pilot trials at Stockholm’s largest wastewater treatment plant, this study showed that alternative cleaning strategies can reduce chemical use by up to 75% without sacrificing treatment performance. The results further suggest that these alternative strategies could result in cost reductions of up to 70% and a reduction in environmental impacts by as much as 95% for certain indicators. Given that MBRs play a crucial role in addressing increasing treatment demands and advancing circular water management, the outcomes of this study are beneficial for the broader adoption of MBR processes. These results also have implications for existing installations, offering a pathway to more sustainable wastewater treatment. Moreover, the presented cleaning strategies provide significant opportunities for lowering operational costs and reducing the environmental footprint of new and existing MBR installations. Full article

Membrane contactors are among the available technologies that allow a reduction in the amount of ammoniacal nitrogen released into the environment through a process called transmembrane chemical absorption (TMCA). This process can be operated with different substances acting as trapping solutions; however, strong inorganic acids have been studied the most. The purpose of this study was to demonstrate, at laboratory scale, the performance of citric acid as a capturing solution in TMCA processes for recovering ammonia as an organic fertilizer from anaerobic digestor reject water using membrane contactors in a liquid–liquid configuration and to compare it with the most studied solution, sulfuric acid. The experiments were carried out at 22 °C and 40 °C and with a feed water pH of 10 and 10.5. When the system was operated at pH 10, the rates of recovered ammonia from the feed solution obtained with citric acid were 10.7–16.5 percentage points (pp) lower compared to sulfuric acid, and at pH 10.5, the difference decreased to 5–10 pp. Under all tested conditions, the water vapor transport in the system was lower when using citric acid as the trapping solution, and at pH 10 and 40 °C, it was 5.7 times lower. When estimating the operational costs for scaling up the system, citric acid appears to be a better option than sulfuric acid as a trapping solution, but in both cases, the process was not profitable under the studied conditions. Full article

The performance of nano-zero-valent iron for heavy metal remediation can be enhanced via incorporation into bimetallic carbon composites. However, few economical and green approaches are available for preparing bimetallic composite materials. In this study, novel Co/Fe bimetallic biochar composites (BC@Co/Fe-X, where X = 5 or 10 represents the CoCl₂ concentration of 0.05 or 0.1 mol L⁻¹) were prepared for the adsorption of Pb²⁺. The effect of the concentration of cross-linked metal ions on Pb²⁺ adsorption was investigated, with the composite prepared using 0.05 mol L⁻¹ Co²⁺ (BC@Co/Fe-5) exhibiting the highest adsorption performance. Various factors, including the adsorption period, Pb²⁺ concentration, and pH, affected the adsorption of Pb²⁺ by BC@Co/Fe-5. Further characterisation of BC@Co/Fe-5 before and after Pb²⁺ adsorption using methods such as X-ray diffraction and X-ray photoelectron spectroscopy suggested that the Pb²⁺ adsorption mechanism involved (i) Pb²⁺ reduction to Pb⁰ by Co/Fe, (ii) Co/Fe corrosion to generate Fe²⁺ and fix Pb²⁺ in the form of PbO, and (iii) Pb²⁺ adsorption by Co/Fe biochar. Notably, BC@Co/Fe-5 exhibited excellent remediation performance in simulated Pb²⁺-contaminated water and soil with good recyclability. Full article

The primary objective of this study is to investigate and develop a rapid and effective method for the immobilization of Sr in the event of a nuclear leakage incident. Coal gangue, an underutilized form of solid waste from the coal industry, can be used as a raw material for curing Sr due to its high content of silica–alumina oxides. In the present study, Sr was successfully solidified in cancrinite synthesized using a hydrothermal method with coal gangue as raw material. A stable cancrinite phase was formed at a relative alkali concentration of more than 6 M. When the Sr/Al(Si) ratio was <1/6, cancrinite was the only stable phase that varied with the hydrothermal temperature and time. When the Sr/Al(Si) ratio increased to 1/2, the cancrinite phase completely disappeared, and a new strontium feldspar phase (SrAl₂Si₂O₈) appeared. PCT leaching experiments showed that when Sr/Al(Si) < 1/6, the Sr leaching rate of Sr-cancrinite samples obtained by hydrothermal synthesis at 180 °C for 24 h was very low. Full article

Blackwater (BW) is a vital source of bio-energy and nutrients for the sustainable development of human society in the future owing to its organic and nutrient-rich properties. Therefore, biomass and water must be used properly to avert environmental challenges and promote the viable development of nutrient recovery and bioenergy production. Moreover, vacuum-collected BW (VCBW) as a renewable source can offer outstanding potential in bioenergy and nutrition sustainability. This review reports previous and present investigations on decentralized wastewater, water conservation, the recovery of nutrients, and the ecological implications and economic significance of integrating torrefaction with anaerobic digestion (AD), notably the continuous stirred tank reactor. The mixtures (torrefied biomass and VCBW) can be converted into valuable materials by combining torrefaction and AD technology for environmental and economic gains. This way, the heat and energy used in the process could be reused, and valuable materials with high energy contents could be obtained for financial gain. The economic evaluation shows that the minimum selling price of the torrefied biomass to reach breakeven could be reduced from 199 EUR/t for standalone torrefaction to 185 EUR/t in the case of torrefaction integrated with AD. The concept can be applied to an existing waste- or wastewater-treatment facility to create a cleaner and more efficient BW with biomass recycling. However, a comprehensive techno-economic analysis must be conducted: (1) Application of tor-biochar towards vacuum BW in AD process is feasible; (2) Digestate as a soil conditional to improve soil condition is effective; (3) Mesophilic and thermophilic conditions are applicable on AD vacuum BW; (4) Economic significance indicates technological feasibility. Full article

Challenges associated with mesophilic digestate (MD) involve volume, odor, and pathogens, which effective post-digestion treatments can address. The efficiency of MD post-treatment can be enhanced by conditioning with ferric chloride (FeCl₃), hydrogen peroxide (H₂O₂), and polymer. This study aimed to observe the effect of combined chemical conditioning on volume reduction, phosphorus (P) release, odor, and pathogen reduction potential for MD. MD was conditioned with polymer only, polymer and FeCl₃ at pH adjusted to 8.0 with lime (Ca(OH)₂), and a blend of polymer, FeCl₃, and hydrogen peroxide (H₂O₂) at pH 8.0. The results show that adding all three chemicals improved post-treatment efficiency at 2.1 kg/t DS FeCl₃, 2.1 kg/t DS polymer, and 600 mg/L H₂O₂ at pH 8.0, compared with polymer or dual conditioning. At the combined dose, cake solid content, centrate P removal, and odor reduction capability improved compared with raw MD by 20%, 99%, and 66%, respectively. Combined chemical treatment reduced fecal coliform by 98% but does not fulfil class A requirements and showed 50% regrowth potential. The synergic effect of polymer, FeCl₃, H₂O₂, and alkaline pH breakdown EPS, reduced water holding capacity and formed compacted flocs for better water removal and settling. This combination also precipitated P through FeCl₃ while H₂O₂ oxidation curbs odor, enhancing further P removal from centrate. Full article

In line with the strategy of transforming existing municipal wastewater treatment plants (WWTP) from disposal facilities into systems for using domestic wastewater (WW) as a source of energy and raw materials, a concept consisting of chemical, physical, and biological steps has been set up as a pilot project in WWTP Büsnau, Stuttgart, Germany. The key part of the entire process is based on the use of advanced microsieving (MS) to eliminate remaining particulate organic carbon (POC) (mg/L) from the effluent of the primary sedimentation tank (PST). Therefore, in the primary stages of this project, it was necessary to have a broad vision and a true understanding of the particle size distribution (PSD) of municipal WW. As a novel approach, in the present study, the conventional PSD method was optimized by implementing certain modifications, and the tests were conducted in situ. The modified PSD analyses facilitated in-depth investigations of solid–liquid separation at WWTPs and showed that drying samples in the oven can result in a 20% to 30% deviation in the POC (mg/L) removal results. In addition, the idea of the substitution of PSTs with an MS was supported by the results of this study. It was determined that an MS with a pore size of 45 µm to 63 µm can provide the same elimination efficiency as a PST. Another significant outcome of this study was the introduction of suitable mesh sizes for the MS which were coupled with PST in order to extract the maximum amount of POC (mg/L) from the municipal WWTPs without the addition of any chemicals. The results revealed that up to 90% of the TSS (mg/L) and 70% of the COD (mg/L) can be removed if an MS with a mesh size between 4 µm and 20 µm is coupled with a PST. Full article

Municipal sludge biochar (MSBC) can be used to absorb phosphorus in water for waste treatment. Nano-zero-valent zinc (nZVZ) was uniformly attached to MSBC to obtain a highly efficient phosphorus-absorbing composite material, nZVZ–MSBC. Characterization by FTIR, XPS, XRD, and BET showed that nZVZ was uniformly dispersed on the surface of the MSBC. Zinc loading was able to greatly improve the adsorption performance of MSBC for phosphorus. Adsorption experiments illustrated that the adsorption process conformed to the Langmuir model, and the maximum adsorption amount was 186.5 mg/g, which is much higher than that for other municipal sludge biochars. The adsorption process reached 80% of the maximum adsorption capacity at 90 min, and this gradually stabilized after 240 min; adsorption equilibrium was reached within 24 h. The optimum pH for adsorption was 5. The main adsorption mechanism was chemical adsorption, but physical adsorption, external diffusion, internal diffusion, and surface adsorption also played roles. The potential for application as an efficient adsorbent of phosphorus from water was confirmed. In addition, a novel strategy for municipal sludge disposal and resource utilization is provided. Full article